This invention relates to the reclamation of printing ink waste and more particularly to the removal of fibrous material from ink waste to produce an acceptable printing ink.
It is well known there are several methods of applying ink to paper to produce the written word. Two popular methods are "letterpress" and "offset" printing. Each method has its advantages and disadvantages and each utilizes a different type of ink.
In the letterpress process, an ink is applied to a raised character and the character is impressed against a surface to be printed, usually paper, and the imprint of the character is left upon the paper. The ink used in this process is of relatively low pigment concentration and is moderately fluid, having a viscosity similar to a light mineral oil.
Excess ink not transferred in the printing process is termed "waste" and is collected from the press. This waste ink typically contains paper fibers and other contaminants from the paper surface. Typically, this ink waste may be reclaimed by the mechanical filtration of the ink to remove the fibrous contaminants to again be acceptable for printing work.
The second method of printing, termed the offset process, utilizes three printing cylinders. A plate is clamped to a plate cylinder. In rotating, it comes in contact with a dampening roller and then an inking roller. The dampeners wet the plate with water or fountain solution so the non-printing area will repel ink. The inked image is then transferred to a rubber blanket on a blanket cylinder. Paper is printed as it passes between the blanket and impression cylinders. The excess ink not utilized in its printing process is removed and collected as waste. This waste ink contains water from the process in addition to large amounts of paper fiber and lint.
The ink used in this process, hereinafter termed "offset ink", is of a highly viscous or stiff nature and has twice the pigment content of a corresponding volume of letterpress ink. The offset ink does not flow and has a consistency similar to whipped cream. Because of the highly viscous nature of the ink and its corresponding low oil content, when waste fibers absorb oil from the ink the waste offset ink is rendered even more viscous. Further, water intimately mixed with the ink further adds to the thick, stiff, viscous nature of the waste ink. This waste ink cannot be conveniently filtered because of its viscous nature; moreover, the free water found in the waste ink is not capable of being removed by a filter.
Waste ink from the offset printing process is toxic and is traditionally considered a hazardous material rendering it expensive to dispose of safely. Further, printing fluids are rapidly becoming very expensive and economic necessity dictates their maximum utility. For these reasons, it has long been desired to recycle or reclaim this waste ink to be reused in the printing process or, at least, to render the offset ink waste nonhazardous to make its disposal more convenient and less expensive.
Many reclaimation systems have been attempted but only two are utilized at all and none are satisfactory. Each system uses some form of agitation to reduce the waste ink viscosity as well as dilution with virgin ink. Thereafter, the waste ink is either strained or filtered by a convenient method.
One method may be referred to as a mechanical strainer. All waste offset is diluted with virgin ink and passed through a strainer. In general, 10 mesh strainers are used to remove gross contaminants and large pieces of paper. Virtually no entrained lint is removed. A 20 mesh strainer removes gross contaminants and up to 25% of the fiber present in the waste; however, finer strainers such as 40 and 60 mesh are ineffective due to rapid plugging with little improvement in fiber removal.
A second method of offset waste processing uses depth cartridge filters of various designs and micron sizes. These filters are designed to remove large quantities of contaminants compared to surface type strainers. In order to remove 90 to 95% of the fiber content which is necessary to produce a reclaimed ink product of useful quality, 50 micron cartridges would be needed.
Experience has indicated that approximately one to one-and-a-half cartridges are needed per gallon of waste ink clarified. This figure varies depending on pressure and type of cartridges, but these differences are not significant. Since the cost of cartridges vary from $1.50 to $2 per unit, the cost of reclaimed ink is $1.50 to $3 per gallon before considering the substantial cost of disposing of the ink sludge-filled cartridges. Disposal of ink-containing cartridges requires special handling procedures and is environmentally dangerous. Further, a disadvantage of both mechanical strainers and cartridge filters is that neither can remove entrained water from the waste offset.
The disadvantages of prior art are overcome by the present invention, however, and improved methods are provided for reclaiming offset printing waste to produce an acceptable offset printing ink.